Graphite brush.



W. H. HARDMAN.

GRAPHITE BRUSH APPLICATION FILED MAY 31, 1912.

1,040,31 5, Patented Oct. 8, 1912.

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STATES PATENT "amnion.

WILLIAM H. HABDMAN, OF- SCHENECT ADY, NEW YORK, ASSIGNOR '10 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

GRAPHITE inusn.

Specification of Letters Patent.

Patented Oct. 8. 1912.

To all whom it-may concern:

Be it known that I, WILLIAM H. HARD- MAN, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Graphite Brushes, of which the following is a specification.

The present invention relates to current collectors and comprises a' substantially allgraphite brush, suitable particularly for direct-current commutating machines.

Although graphite has a higher conductivity than other forms of carbonaceous material, it has not been suitable for all conditions of service because of its soft texture. Particularly when used on commutating machines it is found to be too soft to keep down the mica uniformly with the copper of the commutator, and consequentlyunless the mica is undecut the brush soon chatters, or vibrates up and down on the commutator, causing destructive sparking. Apparently the high mica is due both to unequal abrasion of the mica between the copper and to a mechanical working out of the mica between the copper bars by centrifugal action. It has been necessary to prevent chattering to add to the graphite other forms of carbon, such as lamp-black and coke, so as to increase the hardness of the brush. These additions represent a considerable part of the brush and necessarily materially lower its conductivity.

I have discovered that the advantage of the high conductivity of graphite can be secured, without incurring the difiiculty of high mica, by adding a small amount of finely divided abrasive to the graphite.

The accompanying drawing shows a brush for dynamo electric machines made in accordance with my invention.

In carrying my invention into effect, a pure graphite produced at high temperature in the electric furnace, or'a ure natural raphite, such as Ceylon grap ite, is mixed with about one (1) to five (5) per cent. of a finely divided abrasive, such as carborundum, co-

rundum or the like. The percentage of abraslve will vary with the design and characteristics of the commutator. In most cases, about 'two (2) er cent. of abrasive is preferable. The mixture is compacted into desired form with a carbonizable binder, such as tar or pitch.

Accordmg to one process of manufacture, the pulverized graphite and abrasive, with about ten (10) per cent. of pitch binderyare ground together in benzol or other liquid solvent for the binder. This treatment thoroughly distributes the binder throughout the mass. The benzol is then evaporated and the caked mass is again pulverized.

The brushes are made from this powder by compacting the same in a mold to a desired form, for example, as shown in thedrawmg.

The molded brushes are fired to carbonize and set the binder. Preferably the brushes.

accordingly brought up to 440 degrees C.

in about ninety hours, at which point the temperature'is maintained for about ten hours. After this baking treatment, the brushes are fired in a porcelain kiln at a temperature of about 1200 to 1400 degrees C. The final firing temperature will 'de-" pend somewhat upon the properties desired inthe finished brush, but I prefer to opei' ate the kiln as nearly. as posible at a temperature of 1350 degrees.

I find that in spite of the presence of the abrasive my improved raphite brush exerts practically no greater a rading effect on the copper bars than a carbon brush. My invention, therefore, secures the combined advantage of the high conductivity of graphits and the effect on the mica of a" arder brush. I

WhatI claim as new, and desire to secure by Letters Patent of the United States, is z 1. As an article of manufacture, a current collector consisting substantially of pure graphite and a small amount of abra- In witness whereof, I have hereunto set sive. my hand this 28th day of May, 1912.

2. As an article of manufacture, a current 1 WILLIAM H. HARDMAN. collector consisting of about ninety-eight Witnesses: 5 per cent. (98%) graphite and about two -BENJAMIN B1 HULL,

per cent. (2%) carborundum. 1 HELEN ORFORD. 

